This invention relates to a hot air hem sealer heat exchanger for producing heat seals for sealing a pair of hems in a moving web of thermoplastic film and more particularly to the manufacture of draw tape plastic bags.
Bags made of thin polyethylene materials have been used in various sizes. Small bags are used in the packaging of samples and the like. Larger bags are used as shopping bags; and even larger bags are used for containing trash.
A particularly advantageous closure for such a bag includes a draw tape constructed from the same polyethylene material. U.S. Pat. No. 3,029,853--Piazzi and British Pat. No. 1,125,363--Jortikka are examples of draw tape bags. Such closures have been successfully employed on these bags.
Draw tape closures for large trash bags, and the manufacture of these draw tape trash bags, are described in U.S. Pat. Nos. 2,897.729--Ashton et al, 3,058,402--Kugler, 3,058,403--Kugler, 4,597,750--Boyd et al, 4,617,008--Boyd et al, 4,624,654--Boyd et al, 4,558,463--Boyd and 4,714,454--Herrington.
Draw tape hems have previously been made by various methods. One method is to use a Teflon-coated hot bar which opens and closes against the film in the area of the bag machine where the film starts and stops. The bar closes once during each cycle while the film is stopped. Another method is to use a pair of heated belts to produce a machine-direction seal. Another method is to use a plurality of heated rollers to produce machinedirection heat seals as disclosed in the aforesaid U.S. Pat. No. 4,714,454. Another method is to blow a series of hot air jets against the film as it travels by. One example of this method is disclosed in the aforesaid U.S. Pat. No. 4,558,463.
It is an object of the present invention to seal a pair of hems in a web of film moving at a relatively high speed, such as 250/300 feet per minute, where the seal in the hem is produced by a hot air hem sealer heat exchanger.